Meaning
The mathematical study of the rate at which functional stabilizers and processing aids are consumed or lost from a polymer matrix during thermal stress or environmental exposure. Loss of performance through additive depletion kinetics describes the transformation of active molecules into inactive byproducts or their physical migration out of the plastic.
Consumption Mechanism
Thermal oxidation during the injection moulding cycle often triggers the rapid use of primary antioxidants. These additive depletion kinetics involve bimolecular reactions where stabilizer molecules neutralize free radicals before they can attack the polymer backbone.
Process Limit
High shear environments in the screw and barrel accelerate the loss of internal lubricants. When the concentration of these additives drops below a critical threshold, the melt viscosity increases and the part may show signs of surface burning.
Stability Evaluation
Measuring the oxidative induction time provides a window into the remaining life of the stabilizer package. If the decay rate follows a predictable first order path, the manufacturer can estimate the shelf life of the final product under specific storage conditions. This analysis requires the extraction of additives from the polymer followed by high performance liquid chromatography to determine the exact concentration of the remaining active species.
By comparing these values to the initial loading, the moulder can decide if a batch of material is still suitable for processing or if it has been compromised by improper handling.
